Obviously it varies widely by restaurant and location, but in general I'd agree with the statement that restaurants are a bit louder than they used to be. I'm talking about table service restaurants, rather than fast food. I think the reason is probably that real estate is more expensive now, so restaurants are trying to pack people closer together. Architectural styles are different as well, with spaces being more open, ceilings higher, and more hard surfaces (how many new restaurants have carpet?). There may be differences in people's behavior too, but I can't say that for sure.

For a while during covid, a place I would go to on occasion had full-height plexiglass dividers between each booth. It made such a huge difference in noise, I was sad when they got rid of them.